What E-mail do you use? and why do you not try using Edge browser? it's great!!

yahoo & gmail. I have all my favorites listed in Firefox on a drop down menu and I love it.

You get all that and more on Edge plus you can transfer all your favs over..

How long have you had Windows 10? I had some issues like this happen after my install except I was using Outlook and not Firefox. Have you tried a reboot? That often helps when my pc is acting a little buggy.

" ... it will highlight my word and erase the word or whole sentence before I know it. I lost a half a letter this morning already. ..."

When that happens you might try an "Undo" by holding down the "Ctrl" key and pressing the "z" key.

.

That doesn't help with the accidental "selection" but might at least help you avoid losing work.

.

I had a mouse going bad that behaved similarly to what you're experiencing. Its behavior was the same everywhere though, not just in email.

Try a new mouse, or

Try a different PC (as a test), or

Try a different browser

I tried the UNDO thing when writing today and everything disappeared anyway. I have to left click when moving or activating the curser. Yes I have rebooted, and its even doing it here now. Highlighting the whole sentence. I don't think its a browser problem. I have had windows 10 since February.

If this is a laptop, have you tried disabling the touchpad?

First of all, I would suggest that the window in which you are composing your email should not be a FULL SCREEN. If it is, then make it a little smaller. Second, if you need your mouse cursor inside that window to perform a needed function...then do it. After you're done, move your mouse cursor OUTSIDE OF THAT WINDOW WHILE YOU ARE TYPING. Now...do you still have the same problem?

its a desktop

Jo-Ann - I have been having a similar problem to you. (I have Windows 10 and Firefox, on a desktop computer.) When I highlight one word to move or delete it, all of a sudden the highlighting spreads to a point after or before the word. And then when I hit delete - without looking at what is now highlighted - I lose everything. I have not found a way to make the highlighting "stickier" but I think that is what is needed. (Haven't found it because I have not had the time to look for something that I do not even know exists.)

HTH.

Mine is still doing it. I can't figure out how to stop it.

Anything here that may shed light or give another idea on something else to try.

https://groups.google.com/forum/#!topic/gmail-users/mvBubY1S1dg

Have you tried clicking insert key on your kb, incase you accidently hit it by accident.

JoAnn - Mine is still doing it too and I have not figured out how to stop it either.

I will try all the suggestion from the link and let you know. Thanks

BTW I have never ever used the insert key before

I understand but any key can be tapped accidently

The CNET link below is about strange highlighting behavior Windows users were experiencing a number of years ago. Since no solution has cropped up, you might want to try the simultaneous left-right shift key maneuver from the link that so many found to be a solution. Also note that another person found the combo of Windows button+shift worked.

Elsewhere I read that reducing the resolution of the monitor solved a highlight problem.

I empathize with you...what a frustrating problem!

http://www.cnet.com/forums/discussions/strange-highlighting-problem-with-xp-230534/

June

Its still doing it, I haven't found way to stop it yet.

Still doing it, so frustrated with this!! You will be typing in email or really anywhere then try to correct something, then it highlights then DELETES it all. its even doing it here. Can anyone figure it out?

At this point I would suggest the ONE FINGER METHOD. If using ONE and ONLY ONE finger still results in the same problem, then there is a hardware or software problem somewhere. If the ONE FINGER METHOD does solve the problem, then I'd suspect your problem is your typing.